Automotive engines exhibit differential thermal expansion, variable combustion pressure, and vibration, all of which effect cyclical movement of the engine cylinder head relative to the engine block. Movement of the cylinder head relative to the engine block induces "creep" of the head gasket and eventual failure.
Known automobile engine head gaskets do not adequately respond to this problem since they usually comprise one or more sheets of compressible gasket material that are generally reinforced by relatively incompressible steel elements which surround each combustion chamber opening. Such conventional head gaskets require a relatively high installation force in that they rely on the stretch of the head bolts to act as springs to maintain a constant compression load on the gasket. However, as the compressible material of the head gasket exhibits deformation or "creep" with lapse of time, bolt stretch is relaxed and consequently the bias on the head gasket is relieved, setting the stage for a leak to occur. It is also to be noted that the metallic portions of known head gaskets are generally relatively thicker than the gasket body which promotes head bending and bore distortion upon assembly. Moreover, the metallic combustion seal about each combustion chamber absorbs a high percentage of the applied load in order to effect sealing, therefore precluding uniform load distribution.
Another problem that has not been fully addressed heretofore is that as temperature of the engine increases the head bolts elongate tending to reduce sealing of the combustion chamber. The optimum solution to this problem is a gasket that expands in direct relation to head bolt elongation.